1. Field of the Invention
The present invention relates to a recording/playback apparatus, and more particularly to an apparatus wherein positions on a magnetic tape are intermittently accessed. Specifically, the invention concerns a high-density recording apparatus of helical scanning type such as a VTR (video tape recorder). Concretely, the invention is especially effective for an apparatus in which, as in the job of editing, the time period expended in causing a magnetic tape to travel to a position for recording or playback is often longer than the time period expended in actually recording or playing back data, and besides, the recording and playback need to be started precisely at desired positions on the magnetic tape while the random positions are iteratively accessed.
2. Description of the Related Art
In the conventional rapid search operation for moving a magnetic tape at high speed to a predetermined position at which recording/playback is to be started, in order to reduce the wear of the magnetic tape and the magnetic head, the tape is caused to travel fast under the condition that tape loading on a rotary cylinder is mechanically released completely or halfway so as to separate or space the tape away from the rotary cylinder. Rough locating is done by conjecturing a current search point in accordance with the ratio between the number of revolution pulses derived from respectively a takeup reel and a supply reel. When the vicinity of the desired position has been detected, the magnetic tape is wound round the rotary cylinder again. Since, however, such an operation requires a time period of several seconds, the long time period is wasted before the start of the recording/playback. Thus, in an editing job, usually the total time period expended in searching for desired positions on the tape accounts for the greater part of the overall handling time period of the VTR.
In this regard, a technique which performs the rapid search without releasing the tape loading is disclosed in the official gazette of Japanese Patent Application Laid-open No. 234278/1985. With this technique, in order to rapidly search for a designated address by utilizing address information recorded on a magnetic tape, an approximate position is detected by reel revolution detection means, and the detected position is corrected with the address information delivered from a magnetic head which is normally held in contact with the magnetic tape, thereby searching for the designated address. This technique, however, does not take it into consideration reducing the wear of the magnetic head and the magnetic tape.
Meanwhile, a technique for preventing the wear of a magnetic head and a magnetic tape is disclosed in the official gazette of Japanese Patent Application Laid-open No. 42422/1992. With the technique proposed here, whether or not the magnetic head is extended from a cylinder into contact with the magnetic tape is determined depending upon the operating modes of a recording/playback apparatus. By way of example, in the playback mode, the magnetic head is extended and is held in contact with the magnetic tape, whereas in the fast forward or rewind mode, the magnetic head is somewhat withdrawn and is not held in close contact with the magnetic tape. Such different degrees of the contact between the head and the tape are achieved by changing the magnitude of the extension of the head from the cylinder. Thus, a frictional force acting on the tape is alleviated in the fast forward or rewind mode, with the intention of protecting the tape and prolonging the service life of the head.
In addition, the official gazette of Japanese Patent Application Laid-open No. 115017/1985 discloses a technique which is intended to reduce the wear of a magnetic tape and a magnetic head similarly to the preceding technique. Herein, the magnetic head and the magnetic tape are held out of contact in an ordinary fast forward or rewind mode. On the other hand, when a predetermined switch is pressed in the fast forward or rewind mode, the magnetic head is extended, and a picture is played back while the magnetic tape is being fast forwarded or being rewound.
Besides, the official gazette of Japanese Patent Application Laid-open No. 57414/1989 discloses a technique which is intended to reduce the wear of a magnetic head and a magnetic tape in a full loading type VTR wherein the magnetic tape and the magnetic head are held in contact even when no picture is recorded or played back as in a fast forward or rewind mode. With this technique, in the fast forward or rewind mode, the magnetic head is withdrawn so as to come out of contact with the magnetic head.
Further, the official gazette of Japanese Patent Application Laid-open No. 28048/1992 discloses a technique which concerns a case where pictures are recorded or played back at different magnetic tape speeds. With this technique, in order to prevent the state of contact between a magnetic tape and a magnetic head from changing in dependency on the magnetic tape speeds, a plurality of modes which are determined by the speeds of the magnetic tape are set beforehand, and the magnitude of extension of the magnetic head is varied in accordance with the modes.
Any of the prior-art techniques for reducing the wear consists in determining whether the magnetic head is extended, in accordance with the operating mode for the purpose of alleviating the frictional force of the head on the magnetic tape. None of these prior-art techniques takes into consideration to precisely detect the start position of the recording or playback in the rapid search for the desired position.
At present, it is required of the helical scanning type apparatus such as a VTR to find out the desired position quickly and precisely without damaging the magnetic tape, in the rapid search.